BMR Formulas Explained: Mifflin-St Jeor vs Harris-Benedict

How the most common BMR formulas work and why your result is always an estimate. Use our BMR calculator for a quick number, then read on if you want the math.

What is BMR?

BMR (basal metabolic rate) is the number of calories your body burns at complete rest to keep you alive — breathing, circulation, cell repair, and so on. It doesn’t include activity or digestion. Because we can’t measure it at home, we use formulas that estimate BMR from your sex, age, height, and weight. All formulas give an estimate, not a measured value.

Mifflin-St Jeor

The Mifflin-St Jeor equation is the one we use in our BMR calculator. It was published in 1990 and is often considered one of the most accurate for most adults when compared to measured resting metabolic rate.

Formula (metric):

  • Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5
  • Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161

Result is in kilocalories per day (kcal/day). It’s a good default choice when you don’t have body fat percentage or other data.

Harris-Benedict (revised)

The Harris-Benedict equation was revised in 1984 and is still widely cited. It tends to give slightly different results from Mifflin-St Jeor — often a bit higher for some people. Some studies suggest Mifflin-St Jeor is closer to measured values on average, but both are reasonable estimates.

Revised formula (metric):

  • Men: BMR = 13.397 × weight (kg) + 4.799 × height (cm) − 5.677 × age (years) + 88.362
  • Women: BMR = 9.247 × weight (kg) + 3.098 × height (cm) − 4.330 × age (years) + 447.593

If you’re curious how your number would look with Harris-Benedict, you can find calculators that offer both; we use Mifflin-St Jeor as the default for simplicity and good accuracy.

Why there's no single "perfect" formula

BMR varies from person to person because of genetics, body composition, and other factors. Formulas only use a few inputs (sex, age, height, weight), so they can’t capture that variation. That’s why any BMR result is an estimate. For most people it’s a useful starting point; you can refine your daily target with our TDEE calculator or Calorie calculator and adjust over time based on how you feel and how your weight changes.

How to use this in practice

Get a quick BMR with our BMR calculator. Then use your daily calorie needs (BMR × activity level) — that’s what our TDEE calculator or Calorie calculator does. From there, set a deficit for weight loss with our Calorie deficit calculator and plan meals with the Product calorie calculator or Calorie table.

Limitations and disclaimer

Disclaimer: This tool is for education only. Results are estimates. For personalised advice, consider speaking with a healthcare provider.

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BMR calculator · TDEE calculator · Calorie calculator · Calorie deficit · All calculators